


higher mathematics

by mimizans



Category: Shiritsu Horitsuba Gakuen, Tokyo Babylon, Tsubasa: Reservoir Chronicle, xxxHoLic
Genre: F/F, Femslash, Femslash February, Gen, Plucky Girl Detective, mentioned Doumeki/Watanuki, mentioned Fai/Kurogane, mentioned Seishirou/Subaru
Language: English
Status: In-Progress
Published: 2016-02-19
Updated: 2016-02-18
Packaged: 2018-05-21 13:58:59
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,746
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/6054231
Author URL: https://archiveofourown.org/users/mimizans/pseuds/mimizans
Summary: <blockquote class="userstuff">
              <p>Plucky Girl Detective Hokuto Sumeragi stars in "The Case of the Phantom Duet Partner"</p>
            </blockquote>





	higher mathematics

**Author's Note:**

> i [mentioned this AU](http://clampisms.tumblr.com/post/117551174175/but-listen-the-possibilities-of-horitsuba-gakuen) almost a year ago and i've been tinkering with it ever since, but it just recently started to take shape. 
> 
> coupla things:  
> 1) set in the same verse as [the stormy kissy douwata fic](http://archiveofourown.org/works/3829450)  
> 2) published in honor of the twins' birthdays and femslash february  
> 3) title is from the splithabit song of the same name, which missed its calling as the soundtrack to a scooby-doo chase sequence

Hokuto thought that the life a plucky girl detective would be more exciting, honestly.

It’s been two weeks since she put up advertisements for her services and the only case she’s had involved a missing bento that it turned out someone had just eaten. She’s not sure it even qualified as a case, looking back, since no one ever actually asked her to help; she just sort of came upon Watanuki-kun screaming his head off, terrifying everyone in the vicinity, and felt obligated to intervene. 

Hokuto is sure that she could be an excellent plucky girl detective, given the chance. After all, her keen observational skills mean that she is always the first to know the good gossip. She’s uncannily good at guessing people’s crushes, and has predicted many a future romantic entanglement. Sometimes she thinks she knows people better than they know themselves - and she’s still sure that she’s right about Fay-sensei and Kurogane-sensei, no matter how much Kurogane-sensei had fumed when she suggested it to him as she ran past during her laps in gym class. He had turned an interesting shade of red and shouted that if she had time to talk, she had time to run, and had given her two more laps to drive home the point, which she thought was pretty unfair. It’s not her fault she’s always right. (She’s not sure yet if she’s going to tell her brother that she’s noticed the nervous, sidelong glances he shoots at the school doctor. Families are different than hot-tempered teachers, she laments with a sigh, and one wrong word to Subaru might mean that he never shoots any kind of glance at anyone ever again. Hokuto will not be responsible for that epic tragedy.)

Her sterling observational skills notwithstanding, Hokuto can admit that maybe she lacks some real-world experience. She’s never been a detective before, so she has no idea if she’s even going about this the right way. Maybe she should be scouring for cases to work instead of waiting for them to come to her? She’s never liked to sit around and wait, she thinks, sitting up straighter in her chair. Tenacity is key. If cases aren’t coming to her, she’ll go out and get cases! The students of this school need her, she’s sure of it, and she’s going to make sure not to let them down.

It's with this uplifting thought that she slings her bag over her shoulder and marches out of the classroom to a symphony of scraping chairs and scuffling feet. 

Out in the hallway, Hokuto feels a hand gently touch her on the shoulder and turns to find Himawari smiling brightly at her, looking every inch a sunflower. Hokuto almost sighs. “I hadn’t seen you yet today, Hokuto-chan,” Himawari says, and Hokuto slows down so that they can walk side by side. “Are you headed to lunch?”

“Yup!” Hokuto replies, smiling back at her. “Wanna come with me?”

“Sure,” Himawari says, glancing around the crowded hallway. “I usually meet Watanuki-kun here, but he mentioned something this morning about having some work to do during his lunch period? He sounded awfully frazzled, so I guess it was important.” 

Hokuto frowns for a moment and thinks, _does she not know...?_ but then a beatific smile spreads over Himawari’s face, and Hokuto has to work hard not to laugh out loud. Of course Himawari knows. She had predicted that particular assignation before even Hokuto had. Hokuto is honestly unsure how anyone _doesn’t_ know at this point, with Watanuki-kun walking around perpetually blushing and Doumeki-kun not bothering to hide the fading hickey on his neck. But hey, she’s not here to judge the school’s population for the fact that they walk around blind to television dramas happening all around them. They’re the ones missing out.

“Ah!” Hokuto exclaims with a grin, grabbing Himawari’s hand. “Then you can help me dig up some mysteries!”

“Dig up some...?” Himawari asks, her brows creasing, but she lets Hokuto pull her along anyway. 

“Mysteries!” Hokuto replies, leading Himawari down the crowded hallway. They go through the double doors and out into the courtyard, a summer breeze tossing Hokuto’s bangs and dancing through Himawari’s long ponytail. 

“I’m a detective,” Hokuto explains, looking back at Himawari. “Or, well, I’m trying to be, but I haven’t had any cases yet.”

“Oh!” Himawari says as they settle down onto a cool patch of grass in the shade of a big maple tree. “A detective. How exciting!”

“You’d think so,” Hokuto replies, tucking her legs underneath her. “But so far it’s been completely boring! Not a mystery to be found.”

“Mysteries, huh?” Himawari muses as she unpacks her lunch. “Well, this may not be anything, but Tomoyo-chan was telling me this morning that she heard some odd sounds when she was rehearsing in the choir room last night.”

Hokuto perks up. “Odd sounds?” she asks.

“Yes,” Himawari says, frowning. “She said that it was like someone else was singing, echoing her, but there wasn’t anyone else in the building.”

“And it wasn’t the room’s acoustics?” Hokuto asks. 

Himawari shakes her head. “No,” she says. “Tomoyo-chan said that she had practiced there tons of times before, even at night when the rest of the school was empty, and she’d never had anything like that happen.” Himawari pauses, tilting her head thoughtfully. “If I didn’t know any better, I’d say it was a ghost. But that’s silly!” she laughs.

“A ghost, huh,” Hokuto muses, staring up at the maple’s thick comforter of green leaves.

Himawari shrugs and smiles. “It might not be exactly what you’re looking for, but it sure is a mystery!”

Hokuto grins at her. “Nope, it’s exactly what I’m looking for, Himawari-chan! You’re the prettiest, cutest anonymous tipster a plucky girl detective could have.”

Himawari’s tinkling bell of a laugh rings out. “Glad I could help, Hokuto-chan!”

And so Hokuto Sumeragi, would-be gumshoe, gets her very first case. 

\-------

“Oh, Hokuto-chan!” Tomoyo says, turning to smile softly at Hokuto, who is standing in the doorway of the music room. “I wasn’t expecting to see you here,” she adds, her gentle smile turning mischievous at the edges.

Hokuto grins at her and steps gingerly into the room. “I hope I’m not interrupting,” she says, looking around at the sheet music arranged in arcs across every surface: desks, chairs, the piano bench, even the floor.

“No, it’s fine. I was finishing up,” Tomoyo says, flipping her long dark hair over her shoulder. She frowns slightly. “I have a recital coming up in a few weeks, and I’m trying to put my pieces together.”

“Any luck?” Hokuto asks, carefully stepping over neatly arranged arcs of paper as she makes her way to the piano. 

“Not yet,” Tomoyo says, shrugging. “But I’m sure it will come to me soon. How can I help you, Hokuto-chan?”

Hokuto smiles brightly. Some people find Tomoyo’s formality off-putting, but it puts Hokuto at ease. While she herself has embraced the kind of casual speech patterns that dominate at Horitsuba Gakuen, she grew up speaking exactly as Tomoyo does. Her brother, on the other hand, has never lost his reflexive politeness, in his speech or in anything else. It’s wonderful to hear him and Tomoyo talk to each other; if Hokuto closes her eyes, she can almost imagine they’re two 60-something friends who’ve met on the way to the market. 

Back on track, Hokuto reminds herself. Muse about class and generational differences in speech patterns later. “You know how I’m a detective now, right?” she begins.

“I’ve seen the fliers,” Tomoyo says, her smile dimpling. “They’re very inspiring. I almost wish I had a mystery just so you could solve it!” She laughs, and it’s low and sweet. Hokuto marvels at the contrast between Tomoyo’s singing voice, high and clear, and her laugh, which is surprisingly deep and quiet. 

“I think you might, though,” Hokuto says, echoing Tomoyo’s laughter. “Himawari-chan told me something odd happened to you when you were rehearsing last night.”

Tomoyo frowns and shuffles the sheet music in her hands. “Oh, the echo? Yes, that was strange.” She pauses and carefully lays her papers down on the piano. “I was doing runs, and suddenly I heard someone singing along with me. I called out and asked if anyone was there, but no one answered. I started up again, but I kept hearing someone singing along. I ended up leaving early because I couldn’t concentrate, and I was a little scared, honestly." Tomoyo purses her lips. "I thought that I'd heard a voice the past few times I practiced late, but it was always far away or indistinct enough that I wrote it off as the air conditioning playing tricks on me.”

“That is extremely weird,” Hokuto agrees, leaning her elbows back against the piano. “Do you think someone was here and they just weren’t answering you?”

“I suppose that’s possible,” Tomoyo says, her brow furrowed, “but I can’t imagine who would do that. The strangest part was that the singing last night didn’t sound like it was coming from somewhere nearby. I honestly thought someone was in the room with me or right outside it.”

“That’s creepy, Tomoyo-chan,” Hokuto says. “Now I really want to figure out what’s going on.”

“Well, I would welcome the help,” Tomoyo says, smiling at Hokuto and dipping her head slightly. A long strand of dark hair falls over her shoulder. “It would be nice to be able to practice late without worrying about a phantom duet partner.”

“Then I’m on the case!” Hokuto says with an enthusiastic thumbs-up. Tomoyo’s warm, low laugh bubbles through the choir room and Hokuto feels an echoing warmth bloom in her chest.

\-------

The dorm room door swings open and hits the wall with a mighty slam that makes Subaru drop his pencil and consider, just for a moment, the possibility that he is having a heart attack.

It’s no cardiac episode, of course. It’s his sister, grinning at him from the threshold, a kind of manic gleam in her eyes. Subaru picks up his pencil and spins his chair to face her, sure now that he will not be getting any more algebra done. 

“Guess what?” Hokuto asks, slightly out of breath, bracing herself on the doorjamb and rocking on her heels.

“What,” Subaru replies, trying his hardest not to make the word a question.

“That’s a pretty lackluster ‘what,’ you know, considering that I just ran here to tell you some amazing, earth-shattering news,” Hokuto replies. She turns up her nose at him and sniffs haughtily, but since she can’t keep the smile off her face, it doesn’t have quite the effect she wants.

“Earth-shattering?” Subaru asks, raising an eyebrow at her.

“Earth-chipping, maybe,” Hokuto amends with a dismissive wave of her hand. “But that’s hardly the point. The point is that I’ve found my first case!”

“For your detective agency?” Subaru clarifies, thinking back to the afternoon last week he spent helping her to paper the campus with fliers advertising her services. Things were way too boring, Hokuto had told him as they used a staple-gun to attach bright pink fliers to telephone poles and notice boards. According to her, the campus needed some excitement and ferreting out mysteries to solve was the perfect way to get it.

Subaru isn’t exactly sure why Hokuto thinks the school is boring; for his part, he often wishes that things would be _more_ boring. There are only so many times you can go on scavenger hunts and run obstacle courses and be locked in classrooms with certain faculty members that you may or may not secretly possibly have feelings for before you start to dread Yuuko-sensei’s voice coming over the loudspeakers.

But Hokuto had been insistent, which she is very good at being, so Subaru had helped her hang up her fliers.

Now, as she is standing in his doorway, looking far too smug and a pinch too excited, Subaru is deeply regretting that decision. 

Hokuto clears her throat, readying her voice for her announcement. “My first case as a plucky girl detective is...” She pauses here and glances at Subaru, probably to make sure that he is properly engaged, “...to discover the truth behind the ghost haunting the high school!”

For a moment, Subaru is sure that he heard her wrong. “The what?” he asks, his eyebrows drawing together.

“The ghost!” Hokuto repeats, her smile growing impossibly wider.

“I hate to, you know,” Subaru says, twisting his hands, and he really does hate to, “but why do you think there’s a ghost in the school? I’ve never seen anything in there. Well,” he amends, tipping his head thoughtfully, “not recently, at least.”

“I know!” Hokuto says, finally falling into the room and hopping up to sit on Subaru’s bed, her bright pink tights clashing horribly with the plaid of his blanket. “That’s why I thought it was so strange! After I heard about it from Tomoyo-chan, I asked Sakura-chan and Watanuki-kun about, and they said that hadn’t seen anything strange either.

“And you’d think,” Hokuto says, pointing at Subaru, “that if there was a ghost, one of the three of you would’ve seen it, or heard it, or something!”

“That’s true.” Subaru nods, his eyes following the jiggling of one of Hokuto’s black patent Mary Janes where it’s hanging off the side of the bed. “The school’s actually been very quiet lately. Spiritually, I mean.”

Hokuto smiles at Subaru. “Which makes me think that this isn’t a ghost at all.”

“What do you think it is?” Subaru asks.

“Oh, it’s Yuuko-sensei,” Hokuto says, waving her hand dismissively. “I just want to know how she’s doing it.”

“Hokuto-chan,” Subaru says slowly, tapping his pencil against his leg gently, “why don’t you just let it go? If you know that Yuuko-sensei is the one fabricating the ghost, then you know how it’s going to end if you get involved.”

Hokuto gapes at him. “Getting locked out on the school roof or being doused in syrup and feathers is nothing compared to the sense of accomplishment we’ll feel when we figure out how she’s doing it!”

Subaru grimaces, images of Kamui red-faced, sticky, and livid rising in his mind. “I’d forgotten about the syrup,” he says.

“Kamui-chan hasn’t,” Hokuto replies. She’s shaking her head, but there’s still a grin on her face. “But you’re going to come with me to the school tonight, right?”

Subaru shakes his head so fast that his hair whips into his face. “No, no, I’m not.”

“Subaru-kun, come on! It’ll be fun!”

“The last time I went to the school with you at night Seishirou-san and I ended up trapped in the chemistry lab until you could find someone to pick the lock!”

“You’re lucky I knew that Syaoran-kun could do it, or I would’ve had to get Yuuko-sensei,” Hokuto says, nodding sympathetically.

“And she probably would’ve just laughed and left us in there,” Subaru mutters darkly. The teachers and administration at Horitsuba Gakuen are weirdly invested in barely controlled chaos and uncomfortable situations as teaching tools. Subaru thinks that if burning the school to the ground meant that one student would learn a valuable life lesson, Yuuko-sensei would do it in a heartbeat. Subaru is extremely hesitant to go into the school building more than he strictly needs to, mostly because he wants to limit his chances of being the one who gets the privilege of learning about himself by surviving an arson. “Get someone else to go with you, Hokuto-chan.”

“There are already other people going with me!” Hokuto assures him, leaning forward expectantly. “C’mon, it’ll be fun, like a big sleepover, except with no sleep.”

“And we’re breaking into the school,” Subaru says with a sigh.

“Only technically,” Hokuto shrugs. “They never lock the building! It’s like they want us to break in.”

“Yuuko-sensei probably does,” Subaru warns.

“Well, I’m taking her up on her challenge.” Hokuto’s grinning and her eyes are gleaming with her particularly inspiring brand of optimistic determination. Subaru realizes belatedly that he’s fighting a losing battle. “You’re gonna come with us, right?”

Subaru sags in his chair. “Alright,” he sighs. He points an accusatory finger at Hokuto. “I just want it on the record that I think this a bad idea.”

“Duly noted,” Hokuto grants, rising from the bed and twirling to the center of the room. “Now, on to more important matters: what exactly does one wear to go ghost hunting?”


End file.
